A known gas laser system has a mirror holding structure including a mirror holder plate in which a reflector mirror is mounted in alignment with the laser discharge tube supported by the frame structure of the system. The mirror holder plate is held in place with respect to the laser discharge tube by the combination of retaining means pressing against the mirror holder plate toward the frame structure and elastic pressing means urging the mirror holder plate away from the frame structure. The elastic pressing means typically uses initially coned or Belleville springs provided between the mirror holding and frame structures and pressing the mirror holder plate against the forces exerted by the retaining means. The mirror holder plate is positioned with respect to the frame structure so that the reflector mirror in the mirror holder plate is aligned with the laser discharge tube by the forces exerted by the retaining means and the opposing forces exerted by the elastic pressing means.
The mirror holding structure of the gas laser system thus constructed has a drawback in that the retaining and pressing means, particularly the pressing means implemented by the Belleville springs, are effective solely in axial directions of the mirror holding structure. If the laser discharge tube is subjected to vibrations or mechanical impacts in directions perpendicular to the axis of tube, the mirror holding structure would be dislocated from its proper position with respect to the laser discharge tube and might cause significant reduction in the power output of the system.
The present invention contemplates elimination of such a drawback of a gas laser system of the described nature and it is, accordingly, an important object of the present invention to provide a gas laser system having an improved mirror holding structure which is effective to cope with vibrations and impacts which may occur in any directions with respect to the gas laser discharge tube of the gas laser system.